Power amplifiers

ABSTRACT

Various aspects of the disclosure provide high power and high efficiency power amplifier systems that can be integrated on a chip using integrated circuit processes such as a standard CMOS and SiGe process. A power amplifier system is disclosed according to one aspect. The power amplifier system comprises a first power amplifier, a Wilkinson power splitter, second-stage amplifiers, and a Wilkinson power combiner. The first power amplifier pre-amplifies an RF input signal. The Wilkinson power splitter then splits the power of the amplified RF signal outputted by the first power amplifier among the second-stage amplifiers. Each of the second-stage amplifiers amplifies the respective RF signal from the Wilkinson power splitter. The Wilkinson power combiner then sums the powers of the amplified RF signals outputted by the second-stage amplifiers and outputs the resulting combined RF signal.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD

The present invention generally relates to amplification, and moreparticularly to power amplifiers.

BACKGROUND

A power amplifier may be used to amplify a radio frequency (RF) signalto drive a load, e.g., an antenna in a transmitter. Integration of highpower and high efficiency power amplifiers using integrated circuitprocesses is challenging due to limitations in integrated circuits suchas lower power supply voltages and low oxide breakdown voltages.

SUMMARY OF THE INVENTION

Various aspects of the disclosure provide high output power and highefficiency power amplifier systems that can be integrated on a chipusing integrated circuit processes such as standard CMOS and SiGe BiCMOSprocesses.

In one aspect, a power amplifier system is disclosed. The poweramplifier system comprises a first power amplifier, a Wilkinson powersplitter, second-stage amplifiers, and a Wilkinson power combiner. Thefirst power amplifier pre-amplifies an RF input signal. The Wilkinsonpower splitter then splits the power of the amplified RF signaloutputted by the first power amplifier among the second-stageamplifiers. Each of the second-stage amplifiers amplifies the respectiveRF signal from the Wilkinson power splitter. The Wilkinson powercombiner then sums the powers of the amplified RF signals outputted bythe second-stage amplifiers and outputs the resulting combined RF signalto a load. By summing the powers of the second-stage amplifiers usingthe Wilkinson power combiner, the power amplifier system is able toachieve higher output power and efficiency using integrated poweramplifiers.

In one aspect, the Wilkinson power splitter and the Wilkinson powercombiner are implemented using a compact lumped Wilkinson architectureto achieve integration of the Wilkinson power splitter and the Wilkinsonpower combiner on a chip.

Additional features and advantages of the invention will be set forth inthe description below, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theadvantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing a power amplifier systemaccording to an aspect of the disclosure;

FIG. 2 is a circuit schematic of a lumped-element Wilkinson powersplitter according to an aspect of the disclosure; and

FIG. 3 is a conceptual diagram showing a power amplifier systemaccording to another aspect of the disclosure.

DETAILED DESCRIPTION

Various aspects of the disclosure provide high output power and highefficiency power amplifier systems that can be integrated on a chipusing integrated circuit processes such as standard CMOS and SiGeprocesses. In one aspect, a power system comprises a first poweramplifier, a Wilkinson power splitter, second-stage amplifiers, and aWilkinson power combiner. The first power amplifier pre-amplifies an RFinput signal. The Wilkinson power splitter then splits the pre-amplifiedRF signal among the second-stage amplifiers. Each second stage-amplifieramplifies the respective RF signal from the Wilkinson power splitter.The Wilkinson power combiner then sums the powers of the amplified RFsignals outputted by the second-stage amplifiers and outputs theresulting combined RF signal to a load, e.g., an antenna. By summing thepowers of the second-stage amplifiers using the Wilkinson powercombiner, the power amplifier system is able to achieve higher outputpower and efficiency. In one aspect, the Wilkinson power splitter andthe Wilkinson power combiner are implemented using a compact lumpedWilkinson architecture to achieve integration of the Wilkinson powersplitter and the Wilkinson power combiner on a chip. This allowsintegration of the power amplifier system on a chip using integratedcircuit processes such as standard CMOS and SiGe processes.

FIG. 1 shows a power amplifier system 110 according to one aspect of thepresent invention. The power amplifier system 110 may be used to amplifythe power of a radio frequency (RF) signal from a source 112 and outputthe resulting power amplified RF signal to a load 115 (e.g., anantenna).

The power amplifier system 110 comprises a first power amplifier 120, aWilkinson power splitter 130, second-stage power amplifiers 140, and aWilkinson power combiner 150. In the example shown in FIG. 1, thesecond-stage power amplifiers 140 comprise a second power amplifier 142and a third power amplifier 147.

The first power amplifier 120 receives an RF input signal from thesource 112, amplifies the RF input signal and outputs the amplified RFsignal to the Wilkinson power splitter 130. The Wilkinson power splitter130 evenly splits the power of the amplified RF signal outputted by thefirst power amplifier 120 between the inputs of the second and thirdpower amplifiers 142 and 147. Each of the second and third poweramplifiers 142 and 147 amplifies the respective RF signal from theWilkinson power splitter 130. The Wilkinson combiner 150 sums the powersof the amplified RF signals outputted by the second and third poweramplifiers 142 and 147 and outputs the resulting combined RF signal tothe load 115.

In one aspect, the first power amplifier 120 may be used to pre-amplifythe RF input signal to compensate for losses associated with theWilkinson power splitter 130 and therefore increase gain. There may belosses in the Wilkinson power splitter 130 due to power splitting andother factors depending on the design of the Wilkinson power splitter130. Other benefits of the first power amplifier 120 are discussedbelow.

In one aspect, the Wilkinson power splitter 130 evenly splits the powerof the RF signal outputted by the first power amplifier 120 between theinputs of the second and third power amplifiers 142 and 147. TheWilkinson power splitter 130 also presents a load impedance (e.g., 50ohms) to the first power amplifier 120 that is matched with theimpedance of the first power amplifier 120. This load matching ensuresmaximum power transfer between the first power amplifier 120 and theWilkinson power splitter 130.

Referring to FIG. 2, the Wilkinson power splitter 130 may be implementedusing a lumped-element Wilkinson power splitter. The lumped-elementWilkinson power splitter 130 comprises first and second LC circuits 222and 227 and a resistor 230. Each LC circuit 222 and 227 comprises oneinductor L and two capacitors C that provide a lumped LC circuitequivalent of a transmission line. The capacitance of each capacitor Cand the inductance of each inductor L may be given as follows:

C=1/√{square root over (2)}·ω·Z ₀  (1)

L=√{square root over (2)}·Z ₀/ω  (2)

ω=2·π·f  (3)

where Z₀ is a desired load impedance of the Wilkinson power splitter 130and f is a desired operating frequency of the power amplifier system110. In one aspect, the load impedance Z₀ is matched with the impedanceof the first power amplifier 120 to ensure maximum power transferbetween the first power amplifier 120 and the Wilkinson power splitter130. The operating frequency f may equal the center frequency of the RFsignal to be amplified.

An advantage of using the lumped-element Wilkinson power splitter 130 isthat it consumes much less chip space than a traditional Wilkinson powersplitter comprising ¼ wavelength microstrip transmission lines. Atraditional Wilkinson power splitter is not suitable for chipintegration at lower frequencies. This is because the dimensions of the¼ wavelength microstrip transmission lines used in a traditionalWilkinson power splitter become much too large at lower frequencies tobe integrated on a chip. This limitation makes a traditional Wilkinsonpower splitter unsuitable for commercial cellular applications. Incontrast, the lumped-element Wilkinson power splitter 130 isconsiderable smaller than an equivalent traditional Wilkinson powersplitter, which allows the lumped-element Wilkinson power splitter 130to be integrated on a chip with the power amplifier 120, 142 and 147 toachieve higher density. With higher density, the output power can beincreased for a given area.

Referring back to FIG. 1, after the Wilkinson power splitter splits thepower of the RF signal between the inputs of the second and third poweramplifiers 142 and 147, each of the second and third power amplifiers142 and 147 amplifies the respective RF signal. As discussed above, theWilkinson power combiner 150 sums the powers of the amplified RF signalsoutputted by the second and third power amplifiers 142 and 147 andoutputs the resulting combined RF signal to the load 115.

The second and third power amplifiers 142 and 147 allow the poweramplifier system 110 to achieve high gain and high output power usingintegrated power amplifiers. The gain of an individual power amplifierin an integrated circuit may be limited by a low power supply voltage, alow oxide breakdown voltage, and/or other limitation. By using two poweramplifiers 142 and 147 and summing their powers with the Wilkinson powercombiner 150, the power amplifier system 110 is able to achieve highgain and high output power using integrated power amplifiers. Forexample, if the output power of each power amplifier 142 and 147 is only½ watt, then the output power of the power amplifier system 110 can beas high as a watt.

The Wilkinson power combiner 150 may be implemented using alumped-element Wilkinson power combiner similar to the lumped-elementWilkinson power splitter 130 shown in FIG. 2 using lumped LC circuitequivalents of transmission lines. The lumped-element Wilkinson powercombiner 150 can be integrated on a chip using integrated inductors andcapacitors that consume much less chip area than equivalent ¼ wavelengthmicrostrip transmission lines. This allows the Wilkinson power combiner150 to be integrated on a single chip with the power amplifiers 120, 142and 147 and the Wilkinson power splitter 130 to achieve a high densitypower amplifier system 110.

In one aspect, the Wilkinson power combiner 150 presents a loadimpedance (e.g., 50 ohms) to each of the second and third poweramplifiers 142 and 147 that matches the impedance of each of the secondand third power amplifiers 142 and 147. This load matching ensuresmaximum gain and efficiency. In addition, when the power amplifiers 142and 147 and the Wilkinson power combiner 150 are integrated on the samechip, the Wilkinson power combiner 150 isolates the outputs of thesecond and third power amplifiers 142 and 147 from package parasitics(e.g., parasitic inductances and/or capacitances from output pads, bondwires, etc.). This prevents the package parasitics from directly loadingthe second and third power amplifiers 142 and 147, which can result inload mismatch and lower efficiency. In this aspect of the presentinvention, the second and third power amplifiers 142 and 147 areinsensitive to package parasitics since they are loaded by the Wilkinsonpower combiner 150 on the same chip.

The lumped Wilkinson power splitter and combiner may be integrated on achip using a standard complementary metal oxide silicon (CMOS) andsilicon-germanium (SiGe) processes. For example, the inductors L of thelumped Wilkinson power splitter and combiner may be implemented usingintegrated spiral inductors, slab inductors or other type of integratedinductor. This allows the lumped Wilkinson power splitter and combinerto be integrated with the power amplifiers 120, 142 and 147 on a singlechip to achieve a high density power amplifier system 110 and higherpower output for a given chip area.

In one aspect, the power amplifiers 120, 142 and 147 may be implementedusing Class E or F amplifiers. For example, Class E amplifiers arehighly efficient switching power amplifiers that are capable ofoperating at high frequencies, and may be used to amplify phasemodulated and/or pulse width modulated RF signals. In this aspect, theClass E pre-amplifier 120 improves the power added efficiency (PAE) ofthe power amplifier system 110 by driving the second-stage Class Eamplifiers 142 and 147 into saturation mode. The Class E pre-amplifieralso compensates for any loss in the Wilkinson power splitter 330 andensures that there is a high gain to achieve high PAE.

In another aspect, the power amplifiers 120, 142 and 147 may beimplemented using Class A, B or AB amplifiers. For example, Class ABamplifiers are efficient linear amplifiers, which may be used to amplifyamplitude modulated RF signals such as quadrature amplitude modulation(QAM) signals. It is to be appreciated that the types of amplifiersgiven above are exemplary only and that other types of amplifiers may beused as well.

The amplifier system 110 shown in FIG. 1 may by used as a building blockto build higher power amplifier systems. FIG. 3 shows an example of apower amplifier system 310 comprising first and second amplifier blocks110A and 110B, where each amplifier block 110A and 110B may beimplemented using the amplifier system 110 shown in FIG. 1. Theamplifier system 310 further comprises a power amplifier 320, aWilkinson power splitter 330 and a Wilkinson power combiner 350.

Each amplifier block 110A and 110B comprises a first power amplifier120A and 120B configured to amplify the RF signal from one of theoutputs of the Wilkinson power splitter 330, a Wilkinson power splitter130A and 130B, second-stage amplifiers 140A and 140B, and a Wilkinsonpower combiner 150A and 150B. The operation of each amplifier block 110Aand 110B is explained in the above description of the amplifier system110, and is therefore not repeated here. The output of each amplifierblock 110A and 110B is coupled to one of the inputs of the Wilkinsonpower combiner 350.

The first power amplifier 320 receives an RF input signal from a source(not shown in FIG. 3), amplifies the RF input signal and outputs theamplified RF signal to the Wilkinson power splitter 330. The Wilkinsonpower splitter 330 evenly splits the power of the amplified RF signaloutputted by the power amplifier 320 between the inputs of the first andsecond amplifier blocks 110A and 110B. Each of the first and secondamplifier blocks 110A and 110B amplifies the respective RF signal fromthe Wilkinson power splitter 330. The Wilkinson combiner 350 sums thepowers of the amplified RF signals outputted by the first and secondamplifier blocks 110A and 110B and outputs the resulting combined RFsignal to a load (not shown in FIG. 3). The load may be an antenna.

Thus, a combination of two or more amplifier blocks can be used toachieve higher output power, where each amplifier block may beimplemented using the amplifier system 110 in FIG. 1. In the exampleshown in FIG. 3, the Wilkinson power combiners 150A, 150B and 350 sumthe powers of the amplified RF signals outputted by four poweramplifiers 142A, 147A, 142B and 147B. By summing the powers of fourpower amplifiers 142A, 147A, 142B and 147B, the amplifier system 310 isable to achieve higher output power even when the gain of eachindividual power amplifier may be limited due to device limitations inan integrated circuit. As a result, the power amplifier system 310 isable to provide higher output power without damaging transistors in anintegrated circuit fabricated using bulk sub-micrometer CMOS and SiGeprocesses.

The power amplifier systems according to various aspects of the presentinvention may be used in many applications requiring poweramplification. For example, power amplifier systems according to variousaspects may be used in transmitters to amplify RF signals in the S bandto Q band or other frequency band.

In another example, a power amplifier system according to an aspect maybe used in a wireless mobile device (e.g., cellular phone) to drive anantenna. The high efficiency of the amplifier power system extends thebattery life of the mobile device while achieving high output power. Inthis example, the source of the RF signal may be a component thatperforms frequency up-conversion (e.g., a mixer), a modulator, anotherpower amplifier and/or other component of the mobile device.

In another example, power amplifier systems according to various aspectsmay also be used to drive multiple antennas in a multi-antenna systemsuch as a system with a phased antenna array. In this example, eachpower amplifier system may be used to drive one of the antennas (e.g.,patch antenna) of the multi-antenna system. For the example of a phasedarray, the power amplifier system may amplify RF signals from abeamformer or may be integrated in a beamformer. In this example, thepower amplifiers may be operated in Class E mode to allow for beamshaping in the phased array. The power amplifier systems may also beused to amplify RF signals in a geodesic dome phased array antenna(GDPAA) system that controls numerous radiating elements.

The description is provided to enable any person skilled in the art topractice the various aspects described herein. The previous descriptionprovides various examples of the subject technology, and the subjecttechnology is not limited to these examples. Various modifications tothese aspects will be readily apparent to those skilled in the art, andthe generic principles defined herein may be applied to other aspects.Thus, the claims are not intended to be limited to the aspects shownherein, but is to be accorded the full scope consistent with thelanguage claims, wherein reference to an element in the singular is notintended to mean “one and only one” unless specifically so stated, butrather “one or more.” Unless specifically stated otherwise, the term“some” refers to one or more. Pronouns in the masculine (e.g., his)include the feminine and neuter gender (e.g., her and its) and viceversa. Headings and subheadings, if any, are used for convenience onlyand do not limit the invention.

A phrase such as an “aspect” does not imply that such aspect isessential to the subject technology or that such aspect applies to allconfigurations of the subject technology. A disclosure relating to anaspect may apply to all configurations, or one or more configurations.An aspect may provide one or more examples. A phrase such as an aspectmay refer to one or more aspects and vice versa. A phrase such as an“embodiment” does not imply that such embodiment is essential to thesubject technology or that such embodiment applies to all configurationsof the subject technology. A disclosure relating to an embodiment mayapply to all embodiments, or one or more embodiments. An embodiment mayprovide one or more examples. A phrase such an embodiment may refer toone or more embodiments and vice versa. A phrase such as a“configuration” does not imply that such configuration is essential tothe subject technology or that such configuration applies to allconfigurations of the subject technology. A disclosure relating to aconfiguration may apply to all configurations, or one or moreconfigurations. A configuration may provide one or more examples. Aphrase such a configuration may refer to one or more configurations andvice versa.

The word “exemplary” is used herein to mean “serving as an example orillustration.” Any aspect or design described herein as “exemplary” isnot necessarily to be construed as preferred or advantageous over otheraspects or designs.

All structural and functional equivalents to the elements of the variousaspects described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. No claim element is to be construedunder the provisions of 35 U.S.C. §112, sixth paragraph, unless theelement is expressly recited using the phrase “means for” or, in thecase of a method claim, the element is recited using the phrase “stepfor.” Furthermore, to the extent that the term “include,” “have,” or thelike is used in the description or the claims, such term is intended tobe inclusive in a manner similar to the term “comprise” as “comprise” isinterpreted when employed as a transitional word in a claim.

1.-9. (canceled)
 10. A transmission system, comprising: a first powersplitter having an input, a first output, and a second output, whereinthe power splitter is configured to split the power of a radio frequency(RF) signal received at the input between the first and second outputs;a first amplifier block configured to amplify the RF signal from thefirst output of the power splitter; a second amplifier block configuredto amplify the RF signal from the second output of the power splitter;and a first output power combiner configured to sum the powers of theamplified RF signals outputted by the first and second amplifier blocks;wherein each of the first and second amplifier blocks comprises: a firstpower amplifier configured to amplify the RF signal from the respectiveoutput of the first power splitter; a Wilkinson power splitter having aninput coupled to an output of the first power amplifier, a first output,and a second output, wherein the Wilkinson power splitter is configuredto split the power of the amplified RF signal outputted by the firstpower amplifier between the first and second outputs; a second poweramplifier configured to amplify the RF signal from the first output ofthe Wilkinson power splitter; a third power amplifier configured toamplify the RF signal from the second output of the Wilkinson powersplitter; and a Wilkinson power combiner having a first input coupled toan output of the second power amplifier and a second input coupled to anoutput of the third power amplifier, wherein the Wilkinson powercombiner is configured to sum the powers of the amplified RF signalsoutputted by the second and third power amplifiers and to output theresulting RF signal to the first power combiner.
 11. The power amplifiersystem of claim 10, further comprising a fourth power amplifier coupledto the input of the first power splitter to pre-amplify the RF signalinputted to the first power splitter.
 12. The power amplifier system ofclaim 10, wherein the first power splitter comprises a Wilkinson powersplitter.
 13. The power amplifier system of claim 10, wherein each ofthe first, second and third power amplifiers comprises a Class E orclass F amplifier.
 14. The power amplifier system of claim 10, whereineach of the first, second and third power amplifiers comprises a ClassAB amplifier.
 15. The power amplifier system of claim 10, wherein theWilkinson power splitter is a lumped-element Wilkinson power splittercomprising at least one capacitor and at least one inductor.
 16. Thepower amplifier system of claim 15, wherein the Wilkinson power combineris a lumped-element Wilkinson power combiner comprising at least onecapacitor and at least one inductor.
 17. The power amplifier system ofclaim 10, wherein an output of the first power combiner is coupled to anantenna.
 18. The power amplifier system of claim 10, wherein theWilkinson power splitter has a load impedance that is matched with animpedance at the output of the first power amplifier.
 19. The poweramplifier system of claim 10, wherein the Wilkinson power combiner has aload impedance that is matched with an impedance at the output of eachof the second and third power amplifiers.
 20. The power amplifier systemof claim 10, wherein the first power splitter, the first and secondamplifier blocks and the first power combiner are all integrated on asingle chip.
 21. A transmission system, comprising: a first powersplitter having an input, a first output, and a second output, whereinthe power splitter is configured to split the power of a radio frequency(RF) signal received at the input between the first and second outputs;a first amplifier block having an input coupled to the first output ofthe first power splitter, and an output; a second amplifier block havingan input coupled to the second output of the first power splitter, andan output; a first output power combiner having a first input coupled tothe output of the first amplifier block, a second input coupled to theoutput of the second amplifier block, and an output; and an antennacoupled to the output of the first output power combiner; wherein eachof the first and second amplifier blocks comprises: a Wilkinson powersplitter having an input coupled to the respective output of the firstpower splitter, a first output, and a second output; a first poweramplifier coupled to the first output of the Wilkinson power splitter; asecond power amplifier coupled to the second output of the Wilkinsonpower splitter; and a Wilkinson power combiner having a first inputcoupled to the output of the first power amplifier, a second inputcoupled to the output of the second power amplifier, and an outputcoupled to the respective input of the first output power combiner. 22.The transmission system of claim 21, wherein the Wilkinson powersplitter is a lumped-element Wilkinson power splitter comprising atleast one capacitor and at least one inductor.
 23. The transmissionsystem of claim 21, wherein the Wilkinson power combiner is alumped-element Wilkinson power combiner comprising at least onecapacitor and at least one inductor.
 24. The transmission system ofclaim 21, wherein each of the first and second amplifier blocks furthercomprises a third power amplifier coupled between the input of theWilkinson power splitter and the respective output of the first powersplitter.